Phylogenetic systematics of the Eucarida (Crustacea malacostraca)

Abstract

Ninety-four morphological characters belonging to particular ontogenetic sequences within the Eucarida were used to produce a hierarchy of 128 evolutionary novelties (73 synapomorphies and 55 homoplasies) and to delimit 15 monophyletic taxa. The following combined Recent-fossil sequenced phylogenetic classification is proposed: Superorder Eucarida; Order Euphausiacea; Family Bentheuphausiidae; Family Euphausiidae; Order Amphionidacea; Order Decapoda; Suborder Penaeidea; Suborder Pleocyemata; Infraorder Stenopodidea; Infraorder Reptantia; Infraorder Procarididea, Infraorder Caridea. The position of the Amphionidacea as the sister-group of the Decapoda is corroborated, while the Reptantia are proposed to be the sister-group of the Procarididea + Caridea for the first time. The fossil groups Uncina Quenstedt, 1850, and Palaeopalaemon Whitfield, 1880, are included as incertae sedis taxa within the Reptantia, which establishes the minimum ages of all the higher taxa of Eucarida except the Procarididea and Caridea in the Upper Devonian. The fossil group "Pygocephalomorpha" Beurlen, 1930, of uncertain status as a monophyletic taxon, is provisionally considered to belong to the "stem-group" of the Reptantia. Among the more important characters hypothesized to have evolved in the stem-lineage of each eucaridan monophyletic taxon are: (1) in Eucarida, attachement of post-zoeal carapace to all thoracic somites; (2) in Euphausiacea, reduction of endopod of eighth thoracopod; (3) in Bentheuphausiidae, compound eyes vestigial, associated with abyssal life; (4) in Euphausiidae, loss of endopod of eighth thoracopod and development of specialized luminescent organs; (5) in Amphionidacea + Decapoda, ambulatory ability of thoracic exopods reduced, scaphognathite, one pair of maxillipedes, pleurobranch gill series and carapace covering gills, associated with loss of pelagic life; (6) in Amphionidacea, unique thoracic brood pouch in females formed by inflated carapace and specialized first pieopod, eclosion in zoea phase, body dorsoventrally depressed, thoracopods reduced and antennular statocyst lost, associated with planktonic life; (7) in Decapoda, double series of arthrobranchiae, laminar rostrum, acute stylocerite, two additional pairs of maxillipedes, three pairs of chelipedes and two pairs of walking legs, associated with nekto-benthonic life; (8) in Penaeidea, dendrobranchiae and post-larval mandibular palp expanded; (9) in Pleocyemata, pleopodal incubation of eggs and eclosion in zoea phase; (10) in Stenopodidea, pereiopodal exopods lost in adults and massive third chelipedes, associated with benthonic life; (11) in Reptantia + Procarididea + Caridea, pleura of second abdominal somite overlapping first and specialized setal brushes on propodus of fourth and fifth pereiopods; (12) in Reptantia, hypertrophied first chelipede, associated with benthonic life; (13) in Procarididea + Caridea, chela lost from third pereiopod and epipod-setobranch complexes for gill cleaning; (14) in Procarididea, chelae lost from first and second pereiopods; and (15) in Caridea, ocellus on ocular peduncle.